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Two thin metallic spherical shells of radii _1 and _2( _1< _2) are placed with their centres coinciding. A material of thermal conductivity K is…

JEE Main 2021 — Physics Thermodynamics

2021mcqhard

Two thin metallic spherical shells of radii r1{r}_{1}r1​ and r2(r1<r2){r}_{2}({r}_{1}<{r}_{2})r2​(r1​<r2​) are placed with their centres coinciding. A material of thermal conductivity KKK is filled in the space between the shells. The inner shell is maintained at temperature θ1{\theta }_{1}θ1​ and the outer shell at temperature θ2(θ1<θ2).{\theta }_{2}({\theta }_{1}<{\theta }_{2}).θ2​(θ1​<θ2​). The rate at which heat flows radially through the material is :

Official previous-year question

Held on 31 Aug 2021 · Verified 6 Jul 2026.

Options

  1. A

    K(θ2−θ1)r2−r1\frac{K({\theta }_{2}-{\theta }_{1})}{{r}_{2}-{r}_{1}}r2​−r1​K(θ2​−θ1​)​

  2. B

    K(θ2−θ1)(r2−r1)4πr1r2\frac{K({\theta }_{2}-{\theta }_{1})({r}_{2}-{r}_{1})}{4\pi {r}_{1}{r}_{2}}4πr1​r2​K(θ2​−θ1​)(r2​−r1​)​

  3. C

    πKr1r2(θ2−θ1)r2−r1\frac{\pi K{r}_{1}{r}_{2}({\theta }_{2}-{\theta }_{1})}{{r}_{2}-{r}_{1}}r2​−r1​πKr1​r2​(θ2​−θ1​)​

  4. D

    4πKr1r2(θ2−θ1)r2−r1\frac{4\pi K{r}_{1}{r}_{2}({\theta }_{2}-{\theta }_{1})}{{r}_{2}-{r}_{1}}r2​−r1​4πKr1​r2​(θ2​−θ1​)​

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